Cathodoluminescence degradation of PLD thin films

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Abstract

The cathodoluminescence (CL) intensities of Y2SiO5:Ce3+, Gd2O2S:Tb3+ and SrAl2O4:Eu2+,Dy3+ phosphor thin films that were grown by pulsed laser deposition (PLD) were investigated for possible application in low voltage
field emission displays (FEDs) and other infrastructure applications. Several process parameters (background gas, laser fluence,
base pressure, substrate temperature, etc.) were changed during the deposition of the thin films. Atomic force microscopy
(AFM) was used to determine the surface roughness and particle size of the different films. The layers consist of agglomerated
nanoparticle structures. Samples with good light emission were selected for the electron degradation studies. Auger electron
spectroscopy (AES) and CL spectroscopy were used to monitor changes in the surface chemical composition and luminous efficiency
of the thin films. AES and CL spectroscopy were done with 2keV energy electrons. Measurements were done at 1×10−6 Torr oxygen pressure. The formation of different oxide layers during electron bombardment was confirmed with X-ray photoelectron
spectroscopy (XPS). New non-luminescent layers that formed during electron bombardment were responsible for the degradation
in light intensity. The adventitious C was removed from the surface in all three cases as volatile gas species, which is consistent
with the electron stimulated surface chemical reaction (ESSCR) model. For Y2SiO5:Ce3+ a luminescent SiO2 layer formed during the electron bombardment. Gd2O3 and SrO thin films formed on the surfaces of Gd2O2S:Tb3+ and SrAl2O4:Eu2+,Dy3+, respectively, due to ESSCRs.